A shock absorber includes a cylinder, a piston, a piston rod, an expansion side chamber, a pressure side chamber, an intermediate pipe, an outer pipe, a suction passage, a rectifying passage, and a damping force variable valve. The piston is slidably inserted into the cylinder. The piston rod is inserted into the cylinder to couple to the piston. The expansion side chamber and the pressure side chamber are defined by the piston. The intermediate pipe covers the outer periphery of the cylinder to form a discharge passage with the cylinder. The outer pipe covers the outer periphery of the intermediate pipe to form a reservoir with the intermediate pipe. The suction passage allows only a flow of operation oil from the reservoir toward the pressure side chamber. The rectifying passage is disposed in the piston, and allows only a flow of operation oil from the pressure side chamber toward the expansion side chamber. The damping force variable valve is disposed between the discharge passage and the reservoir.
During expansion and contraction, the shock absorber causes the actions of the rectifying passage and the suction passage such that the operation oil flows out to the reservoir from the inside of the cylinder through the discharge passage. Adjusting the resistance provided to this flow of the operation oil in the damping force variable valve allows adjusting the damping force generated by the shock absorber (for example, see JP2009-222136A).
Thus, the shock absorber allows adjusting the damping force. This allows generating a damping force appropriate for vibration of a vehicle body, so as to improve the ride comfort in the vehicle. The shock absorber having the damping force variable valve outside the cylinder has an advantage that ensures a stroke length and allows maintaining the mountability on a vehicle compared with a shock absorber having the damping force variable valve inside the piston.